The invention relates to a control device for a drive unit of a windshield wiper system, in particular a windshield wiper system for a motor vehicle. In addition, the invention relates to a method for controlling such a drive unit and to the corresponding windshield wiper system.
Windshield wipers are used in various types of vehicles, including as front and rear windshield wipers in motor vehicles. Typical windshield wiper systems include one or more wiper arms provided with wiper blades which are moved cyclically over the windshield to be cleaned in order to wipe moisture from the windshield. An electronically controlled electric motor, typically a rotating motor, whose movement is converted either directly or via a corresponding transmission into the desired wiping movement, acts as drive for a wiper arm. In this case, the motor needs to apply torques of different levels, depending on the operating situation, in order to move the wiper arm at the desired wiping speed over the windshield. In particular the wiping operation on a dry windshield represents a relatively high load on the motor owing to the high frictional forces acting in the process between the windshield surface and the wiper blade. Since a power which needs to be applied by the drive unit is in principle associated with an energy input in the drive unit and a thermal load on the motor component resulting therefrom, windshield wiper motors are generally equipped with special protective functions, which disconnect the motor in the event that a critical temperature is exceeded. As a result of the temperature rise in the motor, the maximum torque of said motor also decreases measurably. In order to ensure that the desired torque and therefore also the windshield wiper function as such is available in any operating situation, the peak loads on the motor which realistically occur during windshield wiper operation needs to be taken into consideration in the dimensioning of the drive unit. Thus, for example, motors with a higher power than is necessary need to be used in order to ensure possibly also relatively long operation on a dry windshield, where possible without activation of the motor protection function. However, the desire for a high-power windshield wiper drive clashes with the aim of making vehicle components such as the windshield wiper motor as compact and light as possible in order to make effective use of the space available in the vehicle and at the same time to be able to reduce the weight of the vehicle.
DE 102006061679 A1 has disclosed a device for driving a drive unit of a wiper system which has a protective function against thermal shutdown of the drive unit. In order to avoid shutdown, the wiping frequency of the windshield wiper is set depending on a load variable, which is dependent on the torque to be applied by the drive unit during wiping. In this case, the wiping frequency is reduced as soon as the load variable exceeds a predetermined first threshold value. Correspondingly, the wiping frequency is increased again as soon as the load variable falls below a predetermined second threshold value.